ATHENS, Greece - In an incident that has been denounced across Greece as an "attack on democracy," a powerful bomb exploded outside the office of a major Greek media group on Monday.

The blast, caused by a makeshift explosive device, occurred at 2.35 am local time (00.30 GMT) on Monday, a short while after anonymous warning calls were made to certain media houses in the country.

Athens police told reporters that the bomb exploded outside the building of the Greek broadcaster and newspaper publisher, Skai media group, causing major damage to the building.

Theodoros Chronopoulos, a police spokesman confirmed that the explosion did not cause any injures, but had damaged the facade of the building housing the media office, in a suburb south of Athens.

Chronopoulos revealed that shortly before 2 am, another television staton and news website in the country had received an anonymous call warning about the explosion.

He said, "They said a bomb would go off in 45 minutes and kept repeating this is not a hoax. It was a big explosion."

The police reportedly evacuated the building immediately after receiving the warning calls.

Skai, which is one of the biggest television stations in Greece, is part of the media group that includes a radio station.

The media group is also affiliated with the country's leading daily newspaper, the Kathimerini, with all the employees of the organization working in the same building that was targeted in the attack.

Chronopoulos said that the bomb was concealed inside a backpack that was placed on a barrier along the road right in front of the Skai offices.

He added that the explosion shattered windows up to the sixth floor of the building, covering the entrance of the building in broken glass and debris from the damaged structure, setting off car alarms and covering the entire area in thick smoke.

Major damage was reported within the building too.

Chronopoulos added that the apartment blocks and vehicles parked around the Skai building too have suffered damage due to the explosion.

While the police have not revealed exact details about the type of device used, local media reports said that the bomb contained up to 22 pounds (10 kilograms) of explosives.

So far, no group has claimed responsibility for the attack and the police have refrained from revealing details of possible suspects.

The chief of the National Police Force, Aristeidis Andrikopoulos visited the scene early on Monday, along with counterterrorism officers who launched an investigation into the attack.

In a statement shortly after the attack, Skai resumed reporting and employees of the organization put out a statement saying, "We will not be gagged and will not be intimidated by any threat, in whatever form."

'Democracy will not be gagged'

On Monday, several Greek politicians from all parties visited the site of the explosion and unanimously denounced it as an "attack on democracy."

In a brief statement, the country's President Prokopis Pavlopoulos denounced the attack as "a criminal and provocatively anti-democratic act."

The Greek Prime Minister Alexis Tsipras issued a statement condemning the "attack by cowardly and dark forces against democracy itself."

Referring to the attackers, Tsipras said, "They will not achieve their goal though, neither to terrorize nor to disorient."

Meanwhile, Tsiprass political rival and leader of the conservative New Democracy party, Kyriakos Mitsotakis visited the site of the explosion on Monday and told reporters that the blast was a "side effect of a toxic climate fueled by the leftist-led government."

Mitsotakis said, "Tolerance of violence, from small-scale violence to a terrorist attack, is extremely dangerous," adding that "pluralism and democracy will not be gagged."

Further, the Public Order Minister Olga Gerovasili told reporters in Athens, "This was a strike against democracy. Thankfully, there was only material damage its a relief that no one was hurt following the swift action taken by the police. Democracy is shielded and will not be threatened."

Adding, "We will reinforce our democracy. This incident should give pause to those who leave a path open to terrorism and fascism."

Maria Spyraki, a New Democracy party spokeswoman said, "Press freedom will not be terrorized by anyone."

The economic crisis and austerity program that impacted the country after 2009 led to a rise in political violence in Greece.

Commenting on Monday's attack, experts noted that the country's media, police, banks, businesses, state departments and embassies have previously been targeted in similar attacks by certain domestic groups, including armed far-left and anarchist organizations.

Previously, the far-left group called Popular Fighters Group has carried out similar attacks, targeting the Athens appeals court in 2017 and the offices of the Federation of Greek Industries in 2015 with powerful explosives.

Before both the attacks, the detonations were preceded by warning calls.